1. Field of the Invention
The present invention relates to a fuel supplying system used in engine starting and, more particularly, to a fuel supplying system adapted to be controlled by an electronic device.
2. Description of the Prior Art
In a conventional fuel supplying system the opening degree of a throttle valve is changed, in the start-up of the engine, i.e. at the time of cranking of the engine, in accordance with the engine temperature such that a predetermined negative pressure of, for example, -50 mmHg is generated in a space of an air passage downstream from the throttle valve. Namely, the effective voltage of the battery as the power source for the engine starter and the viscosity of the lubricating oil are the factors that influence the rotation speed of crank shaft during cranking and depend on the temperature of the engine. Thus, the rotation speed of the crank shaft during the cranking is changed essentially in accordance with the change in the engine temperature. In order to maintain a constant negative pressure in the space of the air passage downstream from the throttle valve, it is essential that the opening degree of the throttle valve is changed in accordance with the rotation speed of the crank shaft. To this end, the opening degree of the throttle valve is controlled in accordance with the engine temperature, because the rotation speed of the crank shaft depends on the engine temperature as explained before. Usually, the temperature of engine cooling water circulated in the engine is used as the index for the engine temperature.
In this fuel supplying system, it is necessary that the rate of fuel supply is changed in accordance with a change in the air flow rate so as to maintain a constant air-fuel ratio of the mixture induced into the engine. To make the most of the performance of this system, it is necessary to take into account various factors which influence the performance of this system such as an ability of the starter battery, a mixture pumping efficiency of the piston-cylinder combination working as a pump, a deterioration of the pumping efficiency, an engine temperature, and so forth. Accordingly a required labor is increased when the engine temperature is high, since a demanded opening degree of the throttle valve is large, it takes a long time until the throttle valve is opened to the demanded opening degree thereof, so that the cranking may be started before the demanded opening degree is provided. Furthermore, the electronic device for processing the aforementioned factors and for driving the aforementioned devices is required to have a large capacity and a complicated structure, resulting in increased manufacturing costs.